1. Field of the Invention
This invention relates to a method and apparatus for modulating uniformity of deposited layer thickness. Particularly, this invention is used to overcome a conventional deficiency that the thickness of a deposited layer is non-uniform, which is more serious for plasma enhanced chemical vapor deposition.
2. Description of the Prior Art
Deposition is an important fabricating process for contemporary semiconductor fabrication. Deposition may be in the form of physical vapor deposition which usually is used to form a metal layer or chemical vapor deposition which usually is used to form both a conductor layer and a dielectric layer. Because formation of a layer on a wafer is a basic step of semiconductor fabrication, especially in the formation of a uniform layer for a multi-layers structures, the value of deposition is abidingly increased and it is desired to improve contemporary deposition technology.
The familiar depositing reactor includes single wafer type and batch type, where only one wafer is placed inside the reactor for the former process but several wafers are placed inside the reactor for the latter process. Moreover, for the conventional depositing reactor, reacting elements, such as gases, are transported into the reactor through some holes formed in the walls of the reactor, and the wafer(s) reacts with imported reacting elements to form a deposited layer on the wafer(s). Obviously, because reacting elements do not react with the wafer(s) totally, it is desired to improve efficiency of deposition by directly exposing the wafer(s) under the reacting elements by a shower head that is located inside the reactor and over the wafer(s). To compare with old way that reacting elements only are transported into the reactor, application of a shower head is significantly efficient for most of reacting elements to react with wafer(s) before they flow to other parts of the reactor, and then efficiency of the depositing process is properly improved.
The relation between the shower head and the wafer is briefly illustrated in FIG. 1A, where a qualitative cross-sectional view is provided. As FIG. 1A shows, shower head 10 is over wafer 11 that is held by a wafer carrier and usually is over a heater block, and the shower head is connected to immobile structure 12, such as a wall of the reactor, by several stretch devices 13. Additionally, for current depositing apparatus for which the shower head(s) is used, shower head 10 is parallel to wafer 11. Moreover, in order to precisely control the depositing process, stretch devices 13 can move, extend or shrink together to adjust both the distance and the relative direction between wafer 11 and shower head 10. Herein, FIG. 1B illustrates this case in demonstrating how the relative direction between wafer 11 and shower head 10 is modified, and FIG. 1C and FIG. 1D illustrate theses cases where the direction between wafer 11 and shower head 10 are modified. Herein, the former figure illustrates the case where the distance is decreased and the latter illustrates the case where the distance is increased.
However, an unavoidable deficiency of deposited layer is failure to achieve total uniformity, where the deposited layer is thicker on one side of wafer 11 and is thinner on another side of wafer 11. Herein, non-uniformity of the deposited layer depends on the material of the deposited layer and the variety of the performed depositing process. The deficiency is more obvious and serious for chemical vapor deposition, especially for plasma enhanced chemical vapor deposition, and the deficiency also is more serious and obvious when material of the deposited layer is dielectric, especially for oxide and silicon nitride. Significantly, the deficiency will produce some troubles for the following fabrication process such as photolithography and etching, and the deficiency also decreases the quality of all chips on wafer 11 for wafers on different part of wafer 11 corresponds to different thickness of the deposited layer.
Furthermore, the non-uniform degree of thickness of the deposited layer is dependent on the configuration of the reactor. This can be understood by the following briefly-described result. Whenever configuration of the reactor is not symmetrical or shower head 10 is not located in the center of the reactor, it is natural that the reacting environment is not symmetrical for wafer 11 that the deposited layer is formed, even if the shower head 10 is directly located over it. Thus, these reacting particles are not uniformly distributed on wafer 10. A direct result is the thickness of the deposited layer is not uniform.
Therefore, according to the previous discussion, in order to improve the quality of deposition, it is desired to overcome the deficiency of non-uniform thickness. Moreover, owing to the fact that the configuration of the reactor is complicated and thus it is difficult to provide perfectly symmetrical reacting environment for each wafer that is deposited, it also is desired to provide a simple and practical way to overcome this deficiency.